linux-kernel - Re: kexec breaks with 5.4 due to memzero

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Date:   Mon, 7 Oct 2019 15:40:56 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Arvind Sankar <nivedita@...m.mit.edu>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: kexec breaks with 5.4 due to memzero_explicit

Hi,

On 07-10-2019 15:09, Ingo Molnar wrote:
> 
> * Hans de Goede <hdegoede@...hat.com> wrote:
> 
>> Hi,
>>
>> On 07-10-2019 10:50, Hans de Goede wrote:
>>> Hi,
>>>
>>> On 07-10-2019 05:09, Arvind Sankar wrote:
>>>> Hi, arch/x86/purgatory/purgatory.ro has an undefined symbol
>>>> memzero_explicit. This has come from commit 906a4bb97f5d ("crypto:
>>>> sha256 - Use get/put_unaligned_be32 to get input, memzero_explicit")
>>>> according to git bisect.
>>>
>>> Hmm, it (obviously) does build for me and using kexec still also works
>>> for me.
>>>
>>> But it seems that you are right and that this should not build, weird.
>>
>> Ok, I understand now, it seems that the kernel will happily build with
>> undefined symbols in the purgatory and my kexec testing did not hit
>> the sha256 check path (*) so it did not crash. I can reproduce this before my patch:
>>
>> [hans@...lem linux]$ ld arch/x86/purgatory/purgatory.ro
>> ld: warning: cannot find entry symbol _start; defaulting to 0000000000401000
>> ld: arch/x86/purgatory/purgatory.ro: in function `sha256_transform':
>> sha256.c:(.text+0x1c0c): undefined reference to `memzero_explicit'
> 
> I've applied your fix,

Thank you, unfortunately I was just minutes away from sending a v2
which adds a missing barrier call (not strictly necessary, more future
proofing).

Hopefully you can still pick up v2 instead, let me know if you want
an incremental patch instead.

Regards,

Hans